IMPAIRED GAS MIXING AND LOW LUNG-VOLUME IN PRETERM INFANTS WITH MILD CHRONIC LUNG-DISEASE

The aim of this study was to assess the possible role of gas mixing in efficiency in spontaneously breathing infants with mild chronic lung d isease (CLD) of prematurity in relation to changes in other functional parameters. A simple bedside technique for recording and analysis of multiple breath nitrogen washout curves was applied together with occl usion mechanics. Fifteen preterm infants with mild or moderately sever e CLD were studied at a mean postconceptional age of 35 wk, together w ith 15 healthy preterm infants at the same maturity. All infants breat hed spontaneously, and the test was performed by a continuous bypass f low system, connected to a face mask, a pneumotachograph, and a nitrog en meter. The results showed impaired gas mixing with moment ratios ab ove the 95th percentile of the normal group in 11/15 infants with CLD. Functional residual capacity (FRC) was low in 13/15 infants, but spec ific compliance and resistance of the respiratory system did not diffe r between the groups. As FRC and moment ratios were not correlated, it is suggested that they may reflect different aspects of the pathophys iology in CLD. It is concluded that low FRC and disturbed gas mixing a re characteristic disturbances in CLD at different degrees of severity . The multiple breath nitrogen washout test, followed by moment analys is of end-tidal nitrogen concentrations, is a simple and sensitive met hod for detection of these disturbances and for monitoring purposes.